1. Field of the Invention
The present invention relates to a cathode ray tube, and more particularly, to a cathode of a cathode ray tube that is capable of shortening a warm-up time taken for formation of an image after power is applied to a cathode ray tube by optimally designing a configuration of a cathode of the cathode ray tube.
2. Description of the Background Art
In general, a cathode ray tube is a device to optically implement an image by converting an electric signal to an electron beam and emitting the electron beam to a fluorescent surface. With its excellent display quality compared to its price, the cathode ray tube is favored and widely used.
The cathode ray tube will now be described with reference to the accompanying drawings.
FIG. 1 is view showing a structure of a general cathode ray tube.
As shown in FIG. 1, a general cathode ray tube includes a panel 15, a front glass; a funnel 19, a rear glass, coupled with the panel 15 to form a vacuous space; a fluorescent surface 14 coated at an inner side of the panel and serving as a luminescent material; an electron gun 100 for emitting electron beam 13; a deflection yoke 18 mounted at a position spaced apart from an outer circumferential surface of the funnel 19 and deflecting the electron beam 13 toward the fluorescent surface 14; and a shadow mask 17 installed spaced apart from the fluorescent surface 14.
As shown in FIG. 2, the electron gun 100 includes a cathode 3 generating the electron beam 13 as a heater 2 inserted therein generates heat; a first electrode 4, a control electrode, being disposed at a distance from the cathode 3 and controlling the electron beam 13; a second electrode 5, an accelerating electrode, disposed with a certain space from the first electrode 4 and accelerating the electron beam 13; third electrode 6, fourth electrode 7, fifth electrode 8, sixth electrode 9 and seventh electrode 10 for focusing or accelerating a portion of the electron beam; and a shield cup 11 having a bulb space connector (BSC) which fixes the electron gun 100 to a neck part of the cathode ray tube while electrically connecting the electron gun 100 and the cathode ray tube.
Accordingly, the electron beam 13 is generated from the surface of the cathode 3 by the heat of the heater heated upon receiving power from a stem pin 1, controlled by the first electrode 4, accelerated by the second electrode 5, and focussed or accelerated by the third electrode 6, the fourth electrode 7, the fifth electrode 8, the sixth electrode 9 and the seventh electrode 10, and then emitted toward the fluorescent surface 14 of the panel.
The cathode generating the electron beam will now be described in detail with reference to FIG. 3.
FIG. 3 is a sectional view of the cathode of the cathode ray tube in accordance with the conventional art.
In the conventional cathode ray tube, the cathode 3 includes a cylindrical sleeve 136 having a heater 2 insertedly installed therein; a base metal 135 fixed at an upper end of the sleeve 136, containing a very small amount of reducing agent such as silicon (Si) or magnesium (Mg) and having nickel (Ni) as a main constituent; and an electron emissive layer 131 attached at the upper end of the base metal 135, and comprising an alkaline earth metal oxide such as strontium (Sr) or calcium (Ca) and having barium (Ba) as a main constituent.
The sleeve 136 includes a blackening layer (not shown) having a high thermal radiation rate formed at its inner circumferential surface for increasing a heat transfer by radiation.
The base metal 135 contains 0.02xcx9c0.04 wt % silicon (Si) and 0.035xcx9c0.065 wt % (a very small amount) magnesium (Mg), the reducing agents.
The operation that electrons are generated in the cathode of the cathode ray tube constructed as described above in accordance with the conventional art will now be explained.
First, as the heater 2 insertedly installed in the sleeve 136 is heated, thermochemical reaction takes place between Barium oxide (BaO), the main constituent of the electron emissive layer 131, and the reducing agents such as silicon (Si) and magnesium (Mg) in the base metal 135. This results in generation of free barium.
At this time, electrons are generated from the free barium, and thermochemical reaction equations of the electron generation are as follows:
BaCO3(heated)=BaO+CO2xe2x80x83xe2x80x83(1)
4BaO+Si=2Ba+Ba2SiO4xe2x80x83xe2x80x83(2)
2BaO+Si=Ba+SiO2xe2x80x83xe2x80x83(3)
BaO+Mg=Ba+MgOxe2x80x83xe2x80x83(4)
Ba+Ba2++2exe2x88x92(electron)xe2x80x83xe2x80x83(5)
Meanwhile, recently, as the cathode ray tube is in the tendency of being large-scaled in its size, a cathode current load density is increased to accelerate reduction of the reducing agents such as silicon (Si) and magnesium (Mg) in the base metal 135 which are diffused and supplied to the electron emissive layer 131, shortening the life span of the cathode 3. Therefore, in order to provide a long life span cathode to the cathode ray tube, the thickness (tB) of the base metal 135 is set thick.
That is, the cathode 3 of the conventional cathode ray tube has used a thin base metal 135 with a thickness of 0.5 mm, but a cathode of the recent cathode ray tube with a high cathode current load density uses a base metal 135 with a thickness of up to 0.25 mm to extend the life span of the cathode ray tube.
However, the thickening of the base metal 135 causes lengthening of time for generating electron beams 13 in the cathode 3. As a result, a warm-up time taken for formation of an image after power is applied to the cathode ray tube is delayed.
Therefore, an object of the present invention is to provide a cathode of a cathode ray tube that is capable of shortening time taken for implementing an image after power is applied to a cathode ray tube by quickly transmitting heat generated from a heater to an electron emissive layer by providing an optimum combination of a thickness of a base metal and a thickness of a sleeve of a cathode.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a cathode ray tube having a cathode, the cathode comprising a sleeve with a heater installed therein and a base metal with a side portion covering an outer circumference of the sleeve and an upper surface portion covering an upper side of the sleeve, satisfies the following formula:
tSxe2x89xa6tB1xe2x89xa62tS
wherein tB1 is a thickness of the side portion of the base metal and tS is a thickness of the sleeve.